The present invention relates generally to fluid seals, and more particularly, to improved methods and apparatus for manufacturing particular kinds of fluid seals. Specifically, the invention pertains to methods and apparatus for overcoming prior problems with seals having so-called embedded garter springs within the lip body portions of what are termed composite fluid seals. By "composite seal" is meant a seal having a casing or stiffening portion as well as an elastomeric portion which includes (but is not limited to) an elastomeric seal lip body. In some preferred designs, the rubber also surrounds and encases the entire seal casing to provide a rubber outside diameter and a pair of opposed rubber end faces.
In most seal designs, it is customary for a so-called garter spring to be provided in order to augment the radial load provided by the innate resiliency of the seal lip. The spring is normally positioned in a groove molded into the lip body, radially outwardly of the seal band area. In certain seals, depending upon the application, and the installation process, there has commonly been difficulty with the garter springs "popping out" or separating from the remainder of the seal. This problem has been addressed in a number of ways, some of which are generally satisfactory and others of which have led to still other drawbacks.
It has been suggested that additional auxiliary flanges or the like be provided for this purpose, but this sometimes requires an extra part or additional manufacturing operations. In addition, such a solution can often make initial positioning of the garter spring difficult and time consuming, thus sacrificing the desired feature of simplicity. It has also been proposed to alter the shape of the spring groove so as to provide a lip portion with greatly increased overhang in the spring groove area to minimize a likelihood that the garter spring will undesirably pop out of its intended position of use. However, such designs often call for a rather large overhang or undercut in the finished product, and this in turn renders molding and product removal problematical or difficult. Accordingly, such solutions have not always achieved their hoped-for advantages.
Still further, it has been suggested that the garter spring could be embedded within the seal body in order to make certain that it does not escape from its intended position. This solution has the advantage of certainty that the garter spring cannot escape. However, the various approaches to positioning a garter spring within the mold has led to erratic and often unsatisfactory results in use. For example, in some instances, it was suggested that the garter spring simply be formed and dropped into the molding cavity without conscious positioning except that created by relative sizes and shapes of the mold parts and the size of the spring itself. This approach has not proved satisfactory inasmuch as the springs have sometimes had a tendency to reposition themselves in reaction to the high forces created during molding. The fluent rubber may displace the garter spring from its intended position of use, resulting in a spring that is embedded eccentrically relative to the seal inside diameter.
Still further, in certain prior designs, it has been found that the embedded spring tends to be positioned in such a way that its effectiveness is compromised. Thus, if the spring uses its own inherent resistance to compression in order to be positioned, then it will normally lie in a corner of the closed mold. This positioning may not be desirable, for a number of reasons. Among these are that, if for design reasons, it is desired to move the spring within the body of the rubber, this is difficult or impossible where the spring inherently biases itself towards a corner or outer diameter surface of the mold. Accordingly, while there are postulated advantages to utilizing a garter spring which is embedded in the seal body, the prior designs and methods have not been entirely satisfactory.
According to the present invention, it is possible to provide a spring positioner that will enable a designer to precisely position a garter spring in relation to the mold cavity. Thus, the spring will assume a desired position in the finished product.
Further, according to the present invention, a properly positioned spring can be used to achieve the advantages of making what are in effect different sizes of seals in the same seal mold. Thus, for example, when an ordinary seal of the type having a spring groove is manufactured, after the rubber has been cured and bonded to the casing, the inside diameter of the seal lip commonly shrinks a considerable amount, such as, for example, 0.060 inches on a 3 inch seal. On larger diameter seals, depending on the seal cross section, the shrinkage can be proportionately greater. The so-called residual interference or molded interference which determines the initial radial load of the seal is simply the difference in diameters respectively of the shaft or other part to be sealed and the inside diameter of the seal itself. The radial load increases as the diameter of the sealed part increases, whether this increase is intentional or merely because of tolerance variation.
An ideal oil seal is one that has a controllable radial load, i.e., one which is sufficient to afford sealing but is not so great as to cause excess friction and wear. It has been found that it is possible to restrict or reduce the shrinkage of the seal inside diameter (i.d.) if a garter spring is embedded in the seal body within an appropriate distance from the seal band. Likewise, it has been discovered that, by preloading the garter spring by placing it in tension as positioned, it is possible not only to place the spring where desired, but also, by varying the preload, the spring diameter, and the size of spring wire, the radial load characteristics of the seal as a whole can be controlled.
A consequence of this is that the same mold can be used to produce seals having different as-molded inside diameters and different variations in preload with residual interference.
Because the cost of making different molds for each of a number of slightly different sizes is prohibitive in large diameter seals, the method and apparatus of the invention can provide seals which will fit a number of different applications without the expense of new mold manufacture.
Consequently, in view of the failure of the prior art to provide an optimized embedded garter spring design for radial lip seals, it is an object of the present invention to provide an improved seal of the embedded spring type.
Another object of the invention is to provide an apparatus and method for making improved embedded garter spring type seals.
Yet another object of the invention is to provide a mold for oil seal manufacture wherein the mold includes a spring positioner comprised of a plurality of spaced apart fingers constructed and arranged so as to precisely position the spring during molding.
A still further object of the invention is to provide a mold for oil seal manufacture wherein at least one mold part includes a spring positioning portion comprised of a plurality of fingers adapted to create pockets in the finished product wherein the embedded spring is only superficially surrounded by a web or covering of rubber, while leaving other portions between the pockets or spaces wherein the spring is surrounded by a mass of rubber.
An additional object of the invention is to provide an oil seal wherein the elastomeric lip body includes air and oil side surfaces and an axially inner surface composed of a substantially continuous generally planar end face portion having a large plurality of spaced apart pockets therein, each of the pockets providing a region wherein the spring is not surrounded by a solid mass of rubber and also providing a large number of regions wherein the spring is substantially fully surrounded.
A still further object of the invention is to provide a method of making seals which includes positioning and pre-tensioning a garter spring in a mold cavity using an array of fingers laid out in a precise way, and then filling the cavity with fluid rubber while retaining the spring in its desired position.
Another object of the invention is to provide a mold which will facilitate easy manufacture of embedded spring type seals, and from which the seals may be removed with little or no difficulty.
A further object of the invention is to provide a mold which is capable of producing seals of different molded inside diameters and different radial load characteristics merely by changing the preload on an inserted garter spring or by changing the wire size and coil diameter of the garter spring material.
A still further object of the invention is to provide a method of mold manufacture which permits spring positioners to be made in a variety of ways.
Yet another object of the invention is to provide a method wherein the initial size and radial load characteristics of an oil seal are controlled by varying the assembled inside diameter of the garter spring as a method of adjusting its tension or preload prior to product manufacture.
An additional object of the invention is to provide a mold design wherein the spring positioners may be made in a variety of simple configurations, all of which are easy to manufacture.
The foregoing and other objects and advantages of the invention are achieved in practice by providing an oil seal having a casing and an elastomeric portion including a portion forming an elastomeric seal lip body, a garter spring embedded in the body and positioned radially outwardly of the pair of frustoconical surfaces meeting to define a seal band, with the garter spring being surrounded in part by rubber ribs and in part by thin walled pockets formed in the seal lip body and thus minimally surrounding parts of the spring, with such seal having reduced post-molding shrinkage and modified radial load characteristics.
The invention also achieves its objects by providing a mold having one mold half that includes portions adapted to form one part of the seal lip body including the frustoconical air and oil side surfaces meeting to form a seal band and other portions adapted to position and support a garter spring, such portions including plural spaced apart fingers extending into the molding cavity.
Still further, the invention achieves its objects by providing a method of seal manufacture which includes propositioning and tensioning a garter spring within the seal mold and thereafter filling the molding cavity with fluent, curable elastomer to form a seal with an at least partially embedded garter spring having desired properties of flexure and memory.